1. Field of the Invention
The present invention relates to a jitter injection apparatus, a jitter injection method, a testing apparatus, and a communication chip. More particularly, the present invention relates to a jitter injection apparatus that generates an output signal having an injected jitter.
2. Related Art
As a test item for a high-speed communication device or the like, there is considered a jitter tolerance testing for testing a range of an amount of jitter in which a device under test can normally be operated for a high-frequency jitter injected into an input signal. For example, Electrical Communication Standardization Division in International Telecommunication Union (ITU-T) recommends that it is necessary to inject a jitter with frequency of several hundred MHz into communication data and test a device under test by means of the communication data.
When performing such a testing, there is considered a method for using a pattern generator that generates communication data and a voltage controlled oscillator that generates a clock operating the pattern generator and injecting a jitter into the communication data by performing frequency modulation or phase modulation on this clock.
For example, there is considered a method for adding a signal according to a jitter to be injected on a control voltage being input into the voltage controlled oscillator. Moreover, as another method, there is a method for providing a variable delay circuit in the subsequent stage of the voltage controlled oscillator and controlling a delay amount of the variable delay circuit according to the jitter to be injected.
However, according to the former method, it is difficult to inject a high-frequency jitter into communication data because a range of frequency capable of being followed by the voltage controlled oscillator is low in the degree of dozens of MHz. Moreover, according to the latter method, since it takes time to change a delay amount of the variable delay circuit, it is difficult to inject a high-frequency jitter into communication data.